1. Field of the Invention:
The invention relates to a welding wire feeding apparatus in general, and more particularly the invention provides a welding wire feeding apparatus mounting technique which is particularly well suited for use with an industrial manipulator which includes an extended welding post depending from the "Z" axis for use in deep vessel welding applications.
2. Description of the Prior Art:
The use of robots in arc welding has been and continues to be a significant component of programs dedicated to industrial automation. A particularly attractive feature of robotic welding lies in the fact that it represents true human replacement, and as such, handles standard welding equipment. For very basic applications, all that is needed is a fitting to mount the welding gun which is attached to its long gas lines and wire feed mechanisms onto the robot's hand. All other equipment associated with the arc welder will then operate in a normal fashion as if being manipulated by human operators. The task performed by the robot is mainly to guide the arc welding gun around the programmed path and to signal when it is on station and ready to proceed. The welding unit controller does the rest. However, despite the apparent simplicity involved in moving a welding gun around a given path, welding operations, even by robots, are a very difficult task and present significant challenges in the design of a robot.
The wrist which supports the welding torch must meet certain requirements in order to adequately carry out the welding operation. For example, in on type of weld tracking methodology there is a need for the wrist to provide an oscillation weave of about 3 to 5 millimeters at a frequency of between about 3 to 5 Hz. U.S. patent application Ser. No. 622,293 filed June 19, 1984 entitled "Wrist and Post for Welding Robots" by Swensrud et al. and assigned to the assignee of the present invention teaches a unique welding torch wrist for such applications.
In addition to the size of the supporting wrist, another significant problem in conventional automated welding systems resides in the axis post that supports the wrist and connects the wrist to the main body of the industrial manipulator. The length and configuration of the axis post in combination with the wrist used therewith have a direct impact on the welding capabilities of the automated device and the accessibility of that device to a given job. Heretofore, the results have been that welding can be accomplished, for example, within the inner surface of a vessel. However, the size of the vessel in which welding operations can be effected is limited by both the length and configuration of the post as well as the configuration of the wrist. Additionally, the weave speed of 3 to 5 Hz necessary for certain arc welding operation generates deflection in the post due to the fundamental natural frequency at or near the weave speed. Thus, rather than simply being a matter of upscaling the access post of a welding unit by increasing its length, serious attention to the large deflections developed therein during welding operations must be addressed. A first step toward eliminating the problems associated with axis-post deflection is also taught in the aforedescribed U.S. patent application Ser. No. 622,293.
A necessary mechanism in a system for performing metal arc welding (MIG Welding) is a wire feed unit. This arc welding process generates heat by an arc between a consumable electrode and the weld metal. The electrode is a bare metal, solid wire which is continuously fed from the wire feeder unit to the torch tip. It has been the practice to use stationary wire feed units mounted on the robot. This has become a problem in an application where an extended axis post and thus the torch must rotate to provide a full 360.degree. of welding range. The stationary wire feed unit mount which is conventionally utilized presents severe limitations to extending the flexibility of the welding robot. This is because it is now possible through the teachings of the aforedescribed patent application to provide an extended axis post which can rotate 360.degree. for the complete peripheral welding of a vessel and with the conventional wire feed unit mount, the welding wire is twisted about the extended axis post. Moreover, when a vessel being welded is very deep, the post required is very long. Finally, because of the type of material to be welded, the electrode weld wire often consists of soft metal and this presents limitations in the deliverability of that wire from a fixed wire feed unit location to the torch tip. A proposed solution has been the use of push-pull wire feed systems which are typically associated with low strength, soft electrode wire. Such devices are, however, larger than is desired and because space is limited in such welding operations, the push-pull wire feed system has been found to be unacceptable.
It is, therefore, an object of this invention to provide an improved wire feeder apparatus with orbital mounting arrangement for welding applications in which an industrial manipulator is equipped with an extended welding post onto which a welding device is mounted.
It is another object of this invention to provide an improved welding robot apparatus which permits 360.degree. of welding inside of deep vessels.
It is yet another object of this invention to provide a wire feed unit mounting arrangement which can be utilized in combination with an extended axis post while not affecting the natural frequency of the post which results in unacceptable torch tip amplitudes.